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Faustetal. Environ Sci Eur (2019) 31:66
https://doi.org/10.1186/s12302-019-0239-4
POLICY BRIEF
Prioritisation ofwater pollutants: theEU
Project SOLUTIONS proposes amethodological
framework fortheintegration ofmixture risk
assessments intoprioritisation procedures
undertheEuropean Water Framework Directive
Michael Faust1, Thomas Backhaus2* , Rolf Altenburger3, Valeria Dulio4, Jos van Gils5, Antoni Ginebreda6,
Andreas Kortenkamp7, John Munthe8, Leo Posthuma9,10, Jaroslav Slobodnik11, Knut Erik Tollefsen12,
Annemarie van Wezel13 and Werner Brack3
Abstract
Current prioritisation procedures under the EU Water Framework Directive (WFD) do not account for risks from
chemical mixtures. SOLUTIONS proposes a multiple-lines-of-evidence approach to tackle the problem effectively. The
approach merges all available evidence from co-exposure modelling, chemical monitoring, effect-based monitoring,
and ecological monitoring. Full implementation of the proposed methodology requires changes in the legal text in
adaptation to scientific progress.
Keywords: Water pollutants, Priority substances, Combined exposure, Mixture toxicity, Cumulative risks, European
chemicals legislation, WFD revision
© The Author(s) 2019. This article is distributed under the terms of the Creative Commons Attribution 4.0 International License
(http://creat iveco mmons .org/licen ses/by/4.0/), which permits unrestricted use, distribution, and reproduction in any medium,
provided you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons license,
and indicate if changes were made.
Challenge
As a strategy against chemical pollution, Article 16 of
the EU Water Framework Directive (WFD) [1] requires
the identification of EU-wide priority substances (PS)
selected amongst those pollutants or groups of pollut-
ants presenting significant risks to or via the aquatic envi-
ronment. In addition, EU Member States are required
to identify river-basin specific pollutants (RBSP) (WFD
Article 4 and Annex V). Furthermore, beyond the ful-
filment of EU-wide WFD requirements, national or
regional rules and provisions may require local water
managers to identify site-specific pollutants or groups
of pollutants causing significant local risks. EU-wide pri-
ority substances, RBSPs, and site-specific pollutants are
subject to risk reduction efforts. e aim is to reduce pol-
lution to safe concentration levels, currently formatted
as so-called environmental quality standards (EQS) for
separate chemicals.
Current regulatory procedures for prioritisation [2–4]
and EQS setting [5] are focused on single substances.
Individual pollutants are assessed as if they would occur
in isolation. e fact that they are part of complex multi-
constituent mixtures is largely ignored. However, a mix-
ture of pollutants usually poses a higher risk than each
individual constituent alone, as detailed in a separate
policy brief on mixture risks [6]. As a consequence, com-
pliance with EQS values for single pollutants (PS and
RBSP) may not be sufficiently protective against toxic
effects from combined exposure to multiple chemicals.
is is not just a theoretical assumption but has also been
demonstrated empirically in a study led by the European
Commission’s Joint Research Centre [7].
Open Access
*Correspondence: thomas.backhaus@bioenv.gu.se
2 University of Gothenburg, Carl Skottsbergs Gata 22B,
40530 Gothenburg, Sweden
Full list of author information is available at the end of the article
Content courtesy of Springer Nature, terms of use apply. Rights reserved.
Page 2 of 4
Faustetal. Environ Sci Eur (2019) 31:66
e problem is well recognized but approaches for
tackling it effectively were missing. e EU project
SOLUTIONS, therefore, took up the challenging task
to develop a proposal for an advanced methodological
framework which integrates mixture risk assessments
into prioritisation procedures under the WFD. e pri-
oritisation is important to make river basin management
planning most efficient.
Recommendation
SOLUTIONS proposes a multiple lines-of-evidence
(LOE) approach for the identification of priority mixtures
presenting significant risks and drivers of mixture toxic-
ity dominating the overall risks (Fig. 1). e suggested
methodology is applicable at all scales (EU, river basin,
and site-specific level).
e approach merges evidence from
i. chemical monitoring, in combination with so-
called component-based approaches for mixture
risk assessment and driver identification,
ii. integrated modelling of co-exposure and resulting
mixture risks,
iii. effect-based monitoring, in combination with so-
called effect-directed analyses or related methods
for the identification of causative (groups of) pol-
lutants,
iv. ecological monitoring, (field observations on so-
called biological quality elements), in combination
with possible indications on causative (groups of)
pollutants.
e multiple LOE approach is detailed in a public
SOLUTIONS deliverable [8]. Explanations of individual
techniques are given in dedicated policy briefs on chemi-
cal screening [9] and associated component-based meth-
ods [10], modelling of co-exposures [11] and resulting
mixture risks [6], effect-based methods [12], and ecologi-
cal tools [13].
For developing the approach, SOLUTIONS thoroughly
examined all available concepts and methods for both (i)
the regulatory assessment of risks from chemical mix-
tures and (ii) the integration of such mixture risk assess-
ment methods into prioritization procedures. No single
method was found to provide a comprehensive solution
for the complex problem of assessing risks from pollut-
ant mixtures in the aquatic environment. Every option
has some advantages but also suffers from specific limi-
tations. As the best possible way forward, SOLUTIONS,
therefore, proposes a framework which integrates all
available LOEs on significant risks.
e advanced framework does not replace existing
procedures for single substance prioritisation but inte-
grates them with novel methodological elements into
the suggested multiple LOE approach. Where one or
more lines of evidence identify groups of pollutants
presenting a significant risk, these should be included
in ranking procedures for risk reduction measures.
Criteria for mixture risk ranking may be essentially
the same as those which have been established for sin-
gle substance prioritization, including the frequency
and the extent of threshold exceedances [14]. Where
appropriate, large groups of dozens or hundreds of
Fig. 1 Graphical presentation of the proposed multiple lines-of-evidence approach for the identification of priority substances and priority
mixtures under the EU Water Framework Directive
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Page 3 of 4
Faustetal. Environ Sci Eur (2019) 31:66
co-occurring pollutants may be reduced to few mixture
components or even one single component which can
be demonstrated to explain most of the overall risk, so-
called drivers of mixture risks.
Wherever conclusive evidence on significant risks and
resulting needs for risk reduction cannot be provided
because all LOEs suffer from significant knowledge-gaps,
mixture components of potential concern are not left
unaccounted for but are prioritised for further research
and testing. is principle is adopted from the NOR-
MAN approach for the prioritisation of individual sub-
stances of emerging concern [15].
Implementation
Implementation of the proposed framework for effec-
tively dealing with mixture risks under the WFD requires
changes in the legal text. e following is needed:
• A broader approach to the prioritisation of pollutants
for risk reduction measures, including all substances
that make a significant contribution to an unaccepta-
ble overall risk, irrespective of whether they exceed
individually acceptable levels or not.
• Comprehensive assessments of the chemical status,
including all pollutants at a given site. Currently,
EU wide priority substances and RBSPs are assessed
in isolation. EU wide priority substances define the
“chemical status”, while RBSPs are considered to
affect the “ecological status”. In a real water sample,
however, both types of pollutants occur together and
they may be accompanied by site-specific pollutants.
EU wide priority pollutants, RBSPs, and site-specific
pollutants jointly contribute to the overall mixture
risk. erefore, they need to be assessed together.
• Uniform legal principles and harmonised technical
rules for the assessment and prioritisation of pollut-
ants and pollutant mixtures on different scales such
as EU wide priority substances, RBSPs, and site-
specific pollutants. For example, EQSs or PNECs
or other reference values used by different Member
States for RBSP identification currently differ, some-
times by orders of magnitude [16]. Such inconsist-
encies in single substance assessments render trans-
parent, consistent, and meaningful mixture risk
assessments impossible.
• A clear legal mandate for the establishment of an
effect-based monitoring system, which may be per-
formed in parallel to chemical monitoring or which
may serve as a trigger for targeted chemical monitor-
ing, as detailed in a European technical report [17]
and specifically addressed in a separate Policy Brief
[12].
ese special needs for amendments are part of a
broader array of recommendations for revising the WFD
with the aim to improve the achievement of its protec-
tion and risk reduction goals, as detailed in Brack etal.
[18].
Chemical risk assessment and risk-based prioritisation
are data-hungry exercises. e generation of necessary
input data, however, is not part of the WFD but governed
by other pieces of EU chemicals legislation. In addition
to amending the WFD, complementary measures must,
therefore, be taken to ensure data availability. Currently,
the limited availability of (eco)toxicity data that are con-
sidered reliable for EQS derivation already poses a seri-
ous problem for the assessment of many individual water
pollutants. For conclusive mixture risk assessments, the
lack of such single substance toxicity data is an even more
severe bottleneck [6]. In addition, co-exposure modelling
suffers from the limited availability of chemical use and
emission data [11]. e WFD does not include mecha-
nisms to close any of these data gaps. Strengthening risk
assessments of both individual aquatic pollutants and
pollutant mixtures, therefore, requires cross-cutting ini-
tiatives, including all pieces of EU chemicals legislation
[19] and clearly assigning responsibilities for providing
reliable (eco)toxicity data.
Abbreviations
EQS: environmental quality standards; LOE: lines-of-evidence; PS: priority sub-
stances (in the sense of the WFD); RBSP: river-basin specific pollutants; WFD:
Water Framework Directive.
Acknowledgements
Special thanks are due to all SOLUTIONS advisory board members and many
invited external experts who helped to shape the proposed framework by
their valuable contributions to three SOLUTIONS prioritisation workshops held
in 2014, 2017, and 2018.
Disclaimer
The findings and conclusions in this paper are those of the authors and do not
necessarily represent the view of the governmental agencies or the research
institutions they represent.
Authors’ contributions
All authors contributed to a series of SOLUTIONS prioritisation workshops from
which this Policy Brief emerged. MF drafted the manuscript. All co-authors
helped to refine it and agreed on the final version. All authors read and
approved the final manuscript.
Funding
The research leading to this Policy Brief was part of the SOLUTIONS project
which received funding from the European Union Seventh Framework Pro-
gramme (FP7-ENV-2013) under Grant Agreement No. 603437.
Availability of data and materials
Not applicable.
Ethics approval and consent to participate
Not applicable.
Consent for publication
Not applicable.
Content courtesy of Springer Nature, terms of use apply. Rights reserved.
Page 4 of 4
Faustetal. Environ Sci Eur (2019) 31:66
Competing interests
The authors declare that they have no competing interests.
Author details
1 Faust & Backhaus Environmental Consulting, Fahrenheitstr. 1, 28359 Bremen,
Germany. 2 University of Gothenburg, Carl Skottsbergs Gata 22B, 40530 Goth-
enburg, Sweden. 3 Helmholtz Centre for Environmental Research UFZ, Per-
moserstr. 15, 04318 Leipzig, Germany. 4 Institut National de l’Environnement
Industriel et des Risques (INERIS), 60550 Verneuil-en-Halatte, France. 5 Deltares,
P.O. Box 177, 2600 MH Delft, The Netherlands. 6 Water and Soil Quality
Research Group, Department of Environmental Chemistry, IDAEA-CSIC, Jordi
Girona 18-26, 08034 Barcelona, Spain. 7 Institute of Environment, Health
and Societies, Brunel University London, Kingston Lane, Uxbridge, Middlesex
UB8 3 PH, UK. 8 IVL Swedish Environmental Research Institute, Box 530 21, 400
14 Gothenburg, Sweden. 9 National Institute for Public Health and Environ-
ment RIVM, Bilthoven, The Netherlands. 10 Department of Environmental
Science, Radboud University, Nijmegen, The Netherlands. 11 Environmental
Institute, Okruzna 784/42, 97241 Kos, Slovak Republic. 12 Section of Ecotoxi-
cology and Risk Assessment, Norwegian Institute for Water Research (NIVA),
Gaustadalléen 21, 0349 Oslo, Norway. 13 Institute for Biodiversity and Ecosys-
tem Dynamics, University of Amsterdam, Postbus 94240, 1090 GE Amsterdam,
The Netherlands.
Received: 3 June 2019 Accepted: 8 August 2019
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